The invention relates to a projection lens, in particular for microlithography and having a lens arrangement, according to the type defined in more detail in the preamble of claim 1. The invention also relates to a method for producing microstructured components with the aid of a projection exposure machine.
It is already known from U.S. Pat. No. 4,871,237 to tune a lens as a function of barometric pressure, specifically via the refractive index of a filling gas in the lens interspace. It is possible, for example, to correct spherical aberration, coma and other faults by a suitable combination of interspaces. However, it is a disadvantage of this lens that other faults are initiated with the removal of one error, for example a spherical aberration.
U.S. Pat. No. 4,676,614 discloses a projection exposure machine which comprises a gas chamber to which pressure can be applied. Image errors caused by a change in atmospheric pressure can be compensated by a specific application of pressure.
U.S. Pat. No. 5,559,584 discloses introducing protective gas into the interspace between a wafer and/or a reticle and the projection lens in the case of a projection exposure machine for producing microstructured components.
In the case of lithographic lenses, spherical aberration, inter alia, arises as image error owing to environmental influences, such as change in air pressure, for example. Other parameters are lens heating and compaction, which likewise lead to spherical aberration. Particularly in the case of a high numerical aperture, the absolute value of the spherical aberration becomes very large and no longer tolerable given the required accuracies.
In addition to U.S. Pat. No. 4,871,237, mentioned at the beginning, it is known to compensate barometric and weather-induced pressure changes by wavelength changes in the case of DUV lenses. However, for 365 nm, 193 nm lenses this method no longer functions and specifically the chromatic correction of the lenses, that is to say the use of different materials, causes the different variation in the refractive indices with the wavelength to lead to image errors which cannot be tolerated.
It is also known from practice to compensate residual errors, caused by environmental influences, by using z manipulators, that is to say lens elements which can be actively displaced in the direction of the optical axis. However, it is disadvantageous of this method that in addition to the large outlay required therefore other errors are once again introduced thereby as well.
It is therefore common to all known methods that they more or less effectively compensate spherical aberration but at the same time once again introduce other errors, or act only incompletely. A complicating factor is added when the optical materials used, in particular lenses, consist of different materials such as, for example, calcium fluoride and quartz glass, because this gives rise to differently varying refractive indices over the wavelength, should it be desired to manipulate over the wavelength.